WO2016156589A1

WO2016156589A1 - Aqueous dispersion of particles of at least one thermoplastic polymer, process for preparing it and applications thereof, especially for sizing reinforcing fibres

Info

Publication number: WO2016156589A1
Application number: PCT/EP2016/057260
Authority: WO
Inventors: Brigitte Defoort; Aurélie MALHO RODRIGUES; Sophie FRANCESCHI; Emile Perez
Original assignee: Airbus Defence And Space Sas; Centre National De La Recherche Scientifique
Priority date: 2015-04-03
Filing date: 2016-04-01
Publication date: 2016-10-06
Also published as: EP3277420A1; FR3034423B1; FR3034423A1; US20180094105A1; EP3277420B1

Abstract

The invention relates to the use of giant micelles as shear-thinning agent in an aqueous dispersion of particles of at least one thermoplastic polymer. It also relates to an aqueous dispersion of particles of at least one thermoplastic polymer, comprising giant micelles located around the particles of the thermoplastic polymer(s), and also to a process that makes it possible to prepare this aqueous dispersion. Applications: all fields in which it is desirable to coat a substrate with a thermoplastic film and, in particular, the sizing of reinforcing fibres intended to be incorporated into the composition of parts made of thermoplastic matrix composite materials and, in particular, of structural parts for the aeronautical and space industries.

Description

AQUEOUS DISPERSION OF PARTICLES OF AT LEAST ONE THERMOPLASTIC POLYMER, ITS PREPARATION METHOD AND ITS APPLICATIONS, IN PARTICULAR FOR

ENSIMAGE OF FIBERS REINFORCEMENT DESCRIPTION

TECHNICAL AREA

The invention relates to the field of coating substrates with thermoplastic polymer films.

More specifically, the invention relates to an aqueous dispersion of particles of at least one thermoplastic polymer which has, among other advantages, those of having rheological properties such that it is viscous at rest but fluid under shear - which has , in particular, as a result that it is stable for several hours in the absence of agitation and easily redispersible after destabilization - and lead, after deposition on a substrate and evaporation of the water it contains, to the formation on this substrate a homogeneous thermoplastic film.

In addition, this aqueous dispersion can be prepared by a process which is simple to implement and which does not require the use of additives of high molecular weight, that is to say, in practice, molecular weight greater than 1000 g / mol.

The invention thus also relates to this method of preparation.

The invention can find applications in all fields where it may be desired to coat a substrate with a thermoplastic film, for example to protect this substrate against corrosion, abrasion or other, to modify its surface properties (wettability resistance, adsorption, adhesion, compatibility with another material, etc.), to improve the appearance or to give it a particular finish, or even to decorate it.

However, it finds a particular interest in the field of the sizing of reinforcing fibers intended to enter the constitution of parts in thermoplastic matrix composite materials and, in particular, structural parts for the aerospace industry.

Also, the invention also relates to the use of said aqueous dispersion for coating at least one substrate with a thermoplastic film and, in particular, for sizing reinforcing fibers for thermoplastic matrix composite materials.

STATE OF THE PRIOR ART

Composite materials are heterogeneous materials that make it possible to exploit the exceptional mechanical properties of materials that we do not know how to manufacture in a massive form but only in the form of fibers by embedding them in a polymer matrix which makes it possible to bind the fibers between them, to ensure a distribution of the stresses in the composite materials and to protect the fibers against the chemical aggressions.

A prerequisite for obtaining a high performance composite material is that the bond between the reinforcing fibers and the polymer matrix that constitute it is good. In fact, if the reinforcing fiber / matrix bond is insufficient, then a composite material with poor transverse mechanical properties (such as shear strength) is obtained and, therefore, with very limited possibilities of use, the composite material parts being , in fact, most often intended to work in a tridirectional constraint state.

The fibers which are conventionally used as reinforcing material, such as carbon fibers, naturally have a low adhesion to the polymer matrices.

Also, manufacturers of reinforcing fibers have sought to adapt their fibers to polymers that can be used as dies by manufacturers of composite parts.

This adaptation was carried out in two different and complementary ways: on the one hand, by surface treatments which all aim to create on the surface of the fibers functional groups capable of reacting with chemical functions presented by the polymer (s) of the matrix; these are mainly chemical or electrolytic oxidation treatments but other types of treatment have also been proposed such as plasma heat treatments, electrolytic treatments in acidic or basic medium and type implantation treatments of atoms. If or B; and

* on the other hand, by the use of specific sizes, that is to say by the deposit on the surface of the fibers of a film of a material whose role is to increase the compatibility between the fibers and the polymer or polymers of the matrix, to facilitate the impregnation of the fibers with this or these polymers and to ensure a "hooking-up" between the fibers and the at least one polymer.

It should be noted that sizes are also applied to the reinforcing fibers for purposes other than improving their bond with a polymer matrix such as, for example, that of facilitating their handling, lubricating and protecting them from the abrasion that they can undergo while being rubbed against each other.

To be able to improve the compatibility between reinforcing fibers and a polymer matrix, a size must, itself, be compatible with this matrix, that is to say be of the same chemical nature as it.

Since at present essentially thermosetting resins of the epoxy resin or epoxyvinylester type are used to make the matrices of the composite materials, the sizes proposed to date are for the most part based on an epoxidized polymer.

On the other hand, there are very few sizes intended for matrices consisting of one or more thermoplastic polymers.

However, the use of thermoplastic polymers, and in particular of so-called "thermostable" thermoplastic polymers (because they retain their mechanical properties at a continuous use temperature greater than 150 ° C.) for producing matrices potentially of great interest, especially for the aeronautics and space industries, because, on the one hand, they make it possible to envisage an improvement of the chemical resistance, the resistance to shocks and the aging behavior of composite materials, and, on the other hand, the Composite materials with thermosetting matrix are not recyclable.

It is therefore desirable to have sizes which are adapted to the use of thermoplastic matrices and which are, therefore, themselves based on one or more thermoplastic polymers.

The size of reinforcing fibers is generally made by immersing the parade of these fibers in a bath where there is a sizing formulation, and drying the fibers out of this bath.

For reasons of safety, public health and environmental protection (compliance with Regulation (EC) No 1907/2006 of the European Parliament and the REACH Council), we are increasingly looking for The size is aqueous and not organic.

However, it turns out that thermoplastic polymers and, in particular, thermostable thermoplastic polymers are typically insoluble in water.

The sizing baths based on such thermoplastic polymers can therefore, a priori, only be in the form of aqueous dispersions in which these polymers are present in the form of particles.

To be able to be used as sizing baths on an industrial scale and lead to a good quality sizing, it is desirable that these aqueous dispersions meet a number of requirements.

In particular, they should have stability in the absence of compatible agitation of their use (a few hours are sufficient) while being easily redispersible after destabilization.

It should also be that these aqueous dispersions are sufficiently fluid to spread easily on the surface of the fibers when they are immersed in the sizing bath but that despite this fluidity, the fibers do not drip once out of the sizing bath. The particles of the polymer (s) present in these aqueous dispersions should also be sufficient in addition to being in sufficient quantity (generally it is desirable that the polymer (s) be present at a level of from 0.1% to 1% by weight relative to to the mass of the fibers), have a smallest possible size and, in any case, less than 1 μιη so that these particles can penetrate and insinuate between the elementary filaments which are formed the reinforcing fibers and thus form by coalescence a homogeneous thermoplastic film on the surface of the fibers or elementary filaments after evaporation of the water.

These aqueous dispersions should furthermore have these properties while including as few additives as possible and, above all, while being examples of high molecular weight additives such as viscosity agents (alginates, pectins, carboxymethylcellulose, etc.) which are conventionally used to stabilize aqueous dispersions of particles. Indeed, it is desirable that out of the sizing bath, there remains on the surface of the fibers no compound likely to degrade during the subsequent implementation of the sized fibers to make composite parts and, by the same, to disrupt this implementation, which is possible if the sizing bath comprises only low molecular weight additives, easily removed by calcination during the drying phase of the fibers following their passage through the dye bath. sizing.

Finally, it should be possible to obtain them by a compatible process, both in terms of its implementation and cost, with exploitation on an industrial scale.

Among the works having focused on the development of aqueous dispersions of particles of a thermoplastic polymer for the sizing of reinforcing fibers, mention may be made of the work of Broyles et al. relating to a size based on a powder of a phenoxy polyhydroxyether simply dispersed in water (Polymer 1998, 39 (15), 3417-3424, hereinafter reference [1]), as well as the work of Giraud and al. relating to particle sizes based on polyetherimide or polyetherketoneketone, stabilized with sodium dodecyl sulphate, sodium dioctylsulphosuccinate or benzalkonium chloride (FR-A-2,960,878; Applied Surface Science 2013, 266, 94-99, hereinafter references [2] and [3]).

However, it turns out that the aqueous dispersions of particles proposed by these authors do not meet the requirements mentioned above.

On the other hand, in the course of their work, the inventors have found that the presence of giant micelles in aqueous dispersions of particles of one or more thermoplastic polymers makes it possible to confer on these dispersions rheological properties such that they are viscous. at rest but fluid under shear, which allows them:

on the one hand, to have a certain stability in the absence of agitation while being redispersible, after destabilization, by simple manual or mechanical agitation, and

on the other hand, to spread easily on the surface of a substrate (such as the surface of reinforcing fibers) under the effect of a shear (such as the agitation to which a bath of sizing) while being able to become viscous after stopping this shear.

They have also found that these aqueous dispersions can be obtained by an emulsion / solvent evaporation or solvent dispersion / evaporation process, allowing said aqueous dispersions to comprise thermoplastic polymer particles of very low cut.

And it is on these findings that the present invention is based.

STATEMENT OF THE INVENTION

The invention therefore, first of all, relates to the use of giant micelles as rheofluidifying agent and, in particular, as a stabilizing agent in an aqueous dispersion of particles of at least one thermoplastic polymer.

The invention also relates to an aqueous dispersion of particles of at least one thermoplastic polymer, which is characterized in that it comprises giant micelles which are located around the particles of the thermoplastic polymer or polymers. In the context of the present invention, the terms "giant micelles" must be understood in the sense that they are given in the literature, namely that they are objects which are in the form of cylinders which can to reach several microns in length for a diameter of a few nanometers and which result from the aggregation by self-assembly of surfactant molecules in aqueous solution. In solution, these objects behave analogously to polymers. However, they are likely to break and reform spontaneously under the effect of shear, which has sometimes earned them the nickname "living polymers". These micelles, which are also known as elongated micelles (or "worm-like micelles" in English) have been described by Cates et al. (Journal of Physics: Condensed Matter 1990, 2, 6869-6892, hereinafter reference [4]), Hassan et al. {Current Science 2001, 80 (8), 980-989, hereinafter reference [5]) and Walker (Current Opinion in Colloid & Interface Science 2001, 6, 451-456, hereinafter reference [6]).

According to the invention, the giant micelles preferably comprise molecules of a cationic or zwitterionic surfactant.

As cationic surfactant, it is especially possible to use a salt chosen from:

the alkyltrimethylammonium salts of formula (C _n H 2n + 1) N ⁺ (CH 3) 3, X ^~ (in which n is greater than or equal to 10 and X ^" is an inorganic or organic counterion), such as bromide; decyltrimethylammonium (or CioTAB), dodecyltrimethylammonium bromide (or DTAB), tetradecyltrimethylammonium bromide (or TTAB), hexadecyltrimethylammonium bromide (or CTAB, also called cetyltrimethylammonium bromide), octadecyltrimethylammonium bromide (or OTAB) , decyltrimethylammonium chloride (or CioTAC), dodecyltrimethylammonium chloride (or DTAC), tetradecyltrimethylammonium chloride (or TTAC), hexadecyltrimethylammonium chloride (or CTAC, also called cetyltrimethylammonium chloride), chloride of octadecyltrimethylammonium (or OTAC), hexadecyltrimethylammonium p-tosylate (or CTAT, also called cetyltrimethylammonium p-tosylate), tetradecyltrimethylammonium salicylate (or Ci ₄ TASal), hexadecyltrimethylammonium salicylate (or Ci6TASal, also known as salicylate cetyltrimethylammonium) or cetyltrimethylammonium 3-hydroxynaphthalene-2-carboxylate (or CTAHNC);

the alkyldimethylethylammonium salts of formula (CnH2n + 1) N ⁺ (CH3) 2 (C2H5), X ^" (in which n is greater than or equal to 10 and X ^" is an inorganic or organic counterion), such as hexadecyldimethylethylammonium bromide (or CDMEAB, also called cetyldimethylethylammonium bromide) or hexadecyldimethylethylammonium chloride (or CDMEAC, also called cetyldimethylethylammonium chloride);

- alkylpyridinium salts of formula (Cnh CsHsN H ^ X ^"(wherein n is greater than or equal to 10 and ^X" is an inorganic or organic against ion) such as hexadecylpyridinium bromide (or PBO, also called decylpyridinium bromide), hexadecylpyridinium chloride (or CPC, also known as cetylpyridinium chloride) or hexadecylpyridinium chlorate (or CPCIO3, also known as cetylpyridinium chlorate), and

benzyldimethylammonium salts such as benzyldimethyl (hydrogenated tallow) ammonium chloride (or DMHTC).

As for the zwitterionic surfactant, it may especially be chosen from betaines with a fatty chain (s), typically C10 to C26, such as betaine of erucyldimethylamidopropyl.

According to a preferred embodiment of the invention, the surfactant is a cationic surfactant with a quaternary ammonium group, more particularly an alkyltrimethylammonium salt as defined above and, more preferably, a hexadecyltrimethylammonium salt such as CTAB, CTAC, CTAT or Ci6AASa, preference being given to all the CTACs.

As known per se, the formation of giant micelles by surfactants requires, with a few exceptions, to be added to these surfactants a salt, which may be inorganic (sodium chloride, sodium bromide, potassium bromide for example) or organic (sodium salicylate, sodium phthalate for example), or an organic acid such as salicylic acid, phthalic acid, chlorobenzoic acid or a hydroxynaphthoic acid such as 5-hydroxy-1-naphthoic acid, 6-hydroxy-1-naphthoic acid, 7-hydroxy-1-naphthoic acid, 1-hydroxy-2-naphthoic acid or 3-hydroxy-2-naphthoic acid.

Also, the giant micelles additionally comprise, advantageously, an inorganic or organic salt or an organic acid and, preferably, salicylic acid.

According to the invention, the thermoplastic polymer or polymers may be chosen from any thermoplastic polymer that may be used for coating a substrate with a thermoplastic film. Thus, this or these thermoplastic polymers may in particular be chosen from polyaryletherketones (or PAEK) such as polyetherketones (or PEK), polyetheretherketones (or PEEK) or polyetherketoneketones (or PEKK), polyethyleneimines (or PEthl), polyetherimides (or PEI), polyimides (or PI), polyolefins such as polyethylenes, especially of high density, polypropylenes or copolymers of ethylene and polypropylene, polyamides such as polyamides 6 (or PA-6), 1.1 (or PA-1.1), 12 (or PA-12), 6.6 (or PA-6.6), 4.6 (or PA-4.6), 6.10 (or PA-6.10), 6.12 (or PA-6.12) or polyamides aromatic compounds, in particular polyphthalamides or aramids, thermoplastic polyurethanes (or TPU), polyphenylene sulfide (or PPS), poly (ethylene terephthalate) (or PET), poly (butylene terephthalate) (or PBT), polysulfones such as polysulfones proper (or PSU), polyes thersulfones (or PES) or polyphenylsulfones (or PPSUs), polycarbonates, polyvinyl chloride, polyvinyl alcohol and mixtures of these polymers.

For the sizing of reinforcing fibers for the manufacture of parts made of composite materials and, in particular, of structural parts for the aerospace industry, the thermoplastic polymer or polymers are preferably chosen from thermostable thermoplastic polymers, that is to say in practice among polyaryletherketones, polyetherimides and polysulfones.

In which case, the giant micelles are preferably formed from a mixture of CTAC and salicylic acid molecules, the inventors having, in fact, demonstrated by thermogravimetric analysis, that the CTAC is degraded to 75% by mass. at 150 ° C while salicylic acid is completely degraded at 180 ° C, ie temperatures which are below the degradation temperature typically exhibited by these thermoplastic polymers. It is thus possible to perform the drying of the reinforcing fibers out of the sizing bath at a temperature to eliminate the ¾ mass of the CTAC and the totality of the salicylic acid without affecting the structure of the thermoplastic polymer (s). In addition, the 25% by weight of CTAC, which are not degraded, correspond to a tertiary amine residue which is not likely to disturb the quality of the sizing of the reinforcing fibers or their subsequent implementation for the manufacture of composite material parts.

This mixture of CTAC and salicylic acid, which is preferably an equimolar mixture, is advantageously present in the aqueous dispersion at a concentration ranging from 5 mmol / L to 100 mmol / L and, preferably, from 40 mmol / L to 50 mmol / L. mmol / L.

In all cases, the mass content of the aqueous dispersion of particles or thermoplastic polymers, based on the total mass of this dispersion, ranges from 0.1% to 3%, preferably from 0.1% to 1% and more preferably 0.4% to 0.6%.

As previously mentioned, the aqueous dispersion can be obtained by an emulsion / solvent evaporation or solvent dispersion / evaporation process.

Also, the subject of the invention is also a process for preparing an aqueous dispersion of particles of at least one thermoplastic polymer as defined above, which is characterized in that it comprises:

a) contacting, with stirring, an organic phase comprising the thermoplastic polymer or polymers dissolved or dispersed in an organic solvent, immiscible with water, with an aqueous phase comprising giant micelles; and

b) evaporation of the organic solvent;

whereby the transfer in the form of particles of the thermoplastic polymer (s) from the organic phase to the aqueous phase is obtained. Preferably, the steps a) and b) are carried out simultaneously, the organic solvent being advantageously a volatile solvent at ambient temperature (chloroform, dichloromethane, dichloroethane, ethyl acetate, ethyl formate, cyclohexane, diethyl ether or a mixture of these for example) so that it can be evaporated only under the effect of the agitation to which the organic and aqueous phases are subjected when they come into contact.

In practice, this process is advantageously implemented by adding dropwise the organic phase comprising the thermoplastic polymer or polymers dissolved or dispersed in the organic solvent to an aqueous solution comprising the elements necessary for the formation of giant micelles (namely a surfactant which is preferably a cationic or zwitterionic surfactant as well as optionally an inorganic or organic salt or an organic acid), and this, under strong agitation, (typically greater than 10,000 rpm if using stirring of the Ultra-Turrax ™ type), and maintaining this agitation until complete evaporation of the organic solvent.

The subject of the invention is also the use of an aqueous dispersion of particles of at least one thermoplastic polymer as defined above for coating at least one substrate with a thermoplastic film and, in particular, for the sizing of fibers. reinforcement for thermoplastic matrix composite materials.

According to the invention, the reinforcing fibers may be chosen from all the fibers that may be used as reinforcement in the manufacture of parts made of composite materials. Thus, it may especially be glass fibers, quartz fibers, carbon fibers, graphite fibers, silica fibers, metal fibers such as steel fibers, aluminum fibers or boron fibers, ceramic fibers such as silicon carbide or boron carbide fibers, synthetic organic fibers such as aramid fibers, polyethylene fibers, polyester fibers or poly (p-phenylene) fibers benzobisoxazole), better known by the acronym PBO, natural organic fibers such as hemp fibers, flax fibers or silk fibers, or mixtures of such fibers. The reinforcing fibers are preferably in the form of yarns comprising several thousand elementary filaments (typically from 3000 to 48000), for example measuring 6 to 10 μm in diameter in the case of carbon fibers. This type of fiber is known under the English names "rovings" or "tapes".

Furthermore, the size of the reinforcing fibers preferably comprises the immersion of these reinforcing fibers in the aqueous dispersion and then drying them. Alternatively, however, it can also be achieved by spraying the aqueous dispersion onto the reinforcing fibers and then drying these fibers.

Other features and advantages of the invention will appear better on reading the additional description which follows, which relates to examples of preparation of aqueous dispersions in accordance with the invention and demonstration of their properties, and which is given in reference to the appended figures.

Of course, this additional description is only given as an illustration of the subject of the invention and does not constitute a limitation of this object.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates the evolution of the stability of a first aqueous dispersion according to the invention, as determined by multiple light scattering over a period of 50 hours, this first aqueous dispersion being a dispersion of particles of a polyetherimide.

FIG. 2 illustrates the rheograms of said first aqueous dispersion as established twice, on the one hand, on the day of its preparation (symbols ▲ and Δ) and, on the other hand, after 7 days of rest and redispersion by simple manual agitation (symbols · and O).

FIG. 3 is a transmission electron microscope (TEM) image of said first aqueous dispersion.

FIG. 4 is a scanning electron microscope (SEM) image of a film obtained by depositing said first aqueous dispersion on a graphite plate and drying this plate. Figure 5 is a diagram illustrating the sizing device having been used to size carbon fibers with said first aqueous dispersion.

Figs. 6A and 6B are M EB images of filaments of a carbon fiber which has been sized with said first aqueous dispersion by means of the device shown in Fig. 5 and using a running speed of 10 m / min.

Figs. 7A and 7B are M EB images of filaments of a carbon fiber that has been sized with said first aqueous dispersion by means of the device shown in Fig. 5 and using a running speed of 15 m / min.

FIGS. 8A and 8B are images taken at the EB of filaments of carbon fiber that have not been sized, these images being given for comparison purposes.

FIG. 9 is an image taken at the M EB of a film formed by deposition of a second aqueous dispersion according to the invention on a graphite plate and drying of this plate, this second aqueous dispersion being a dispersion of particles of a polyethersulfone.

FIG. 10 is an image taken at the M EB of a film formed by deposition of a third aqueous dispersion according to the invention on a graphite plate and drying of this plate, this third aqueous dispersion being a dispersion of particles of a polysulfone. DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

EXAMPLE I: Aqueous dispersion of particles of a polyetherimide

1.1 - Preparation of the dispersion:

An aqueous dispersion of particles of a polyetherimide (PEI Ultem ™ 1000 resin - GE Plastics), hereinafter referred to as dispersion 1, is prepared by emulsion / evaporation. This PEI has a glass transition temperature of 217 ° C.

To do this, 0.71 g of the PEI resin is dissolved in 13.6 ml of dichloromethane with magnetic stirring.

At the same time, 1.868 g of cetyltrimethylammonium chloride (CTAC) in 136.4 ml of distilled water are dissolved, also with magnetic stirring. (A concentration of CTAC 4,11.10 ^{~ 2} mol / L) and then added to the solution thus obtained, 0.805 g of salicylic acid (a concentration of salicylic acid also 4,11.10 ² mol / L).

The organic resin solution is added dropwise to the aqueous solution of CTAC / salicylic acid with stirring with Ultra-Turrax ™ - I KA. The addition lasts about 5 minutes. The stirring is set at 12,000 rpm and is maintained until complete evaporation of the dichloromethane, ie for about 30 minutes.

An aqueous dispersion at 0.51% by mass of PEI particles is thus obtained. 1.2 - Properties of the dispersion:

* Particle size:

The average diameter and the polydispersity index of the particles of the dispersion 1 are determined by means of a dynamic light scattering apparatus Zetasizer Nano S - MALVERN I nstruments, using a high power laser (50 mW) emitting at the wavelength of 532 nm and by collecting the light signal scattered by the sample to be analyzed backscattering (173 ° angle). The measurement is carried out at 25 ° C.

The average particle intensity diameter is 209 nm.

Their polydispersity index is 0.265. * Stability of the dispersion:

The stability of the dispersion 1 is assessed by means of a Turbiscan ™ LAB-FORM ULACTION apparatus which makes it possible to precisely and quickly characterize the stability of a liquid dispersion by multiple light scattering (MLS).

Multiple light scattering is a well-known method of sending Remission photons = 880 nm) into the sample to be analyzed. These photons, after having been scattered multiple times by the particles of the dispersion, leave the sample and are detected by two detectors, one in transmission, the other in backscatter (135 ° angle). The analysis is carried out at 25 ° C. The intensity of backscattering is directly related to the photon transport length. Also, does this intensity depend on particle size and concentration.

Monitoring the difference between the intensity of the backscattered light at time t and at time t (R _t o - Rt) is carried out for several days with an interval of 3 hours between each measurement.

1 illustrates, in the form of a curve, the change in the variation of the intensity of the backscatter relative to the intensity of the backscatter at time t (ie (R _t o - Rt) / Rto) denoted AR and expressed in percentages, as obtained for dispersion 1 over a period of 50 hours.

As shown in this figure, the curve shows a change in slope, characteristic of a beginning of sedimentation of the particles from 22 hours. The dispersion 1 begins to destabilize only after 22 hours.

* Rheological analysis of the dispersion:

The dispersion 1 rheology is evaluated by tests that include measuring the viscosity of this dispersion by applying a shear rate of 0.6 s went nt ¹ to 500 s ^"1, and that, on the one hand, the the day of its preparation and, on the other hand, after 7 days of rest and redispersion by simple manual agitation, each test is performed twice.

FIG. 2 illustrates the rheograms thus obtained, the viscosity being expressed in mPa.s and the shear rate in s.sup.- ¹ . In this figure, the symbols ▲ and Δ correspond to the rheograms obtained on the day of the preparation of the dispersion 1 while the symbols · and O correspond to the rheograms obtained after the 7 days of rest of this dispersion.

As shown in FIG. 2, the dispersion 1 exhibits, on the day of its preparation, a viscosity of the order of 800 mPa.s without shear and its viscosity drops to 500 mPa.s from the application of a shear rate. of 1 s ^"1 .

It also shows that it is enough for a simple manual stirring so that the dispersion 1 found, near 7 days of rest, a viscosity close to that it has the day of its preparation. * Microscopic analysis:

As shown in FIG. 3, which corresponds to a TEM image of the dispersion 1, this dispersion comprises spherical particles (present on the image in the form of white circles) which have a maximum diameter of 200 nm, contained in FIG. middle of cylindrical micelles.

The size distribution of these particles is polydisperse (the size of the particles ranging from 20 nm to 200 nm) in agreement with the results obtained by dynamic light scattering.

* Filmoqene properties:

The ability of the dispersion 1 to form a film on a substrate is first tested by depositing a drop of this dispersion on a graphite plate using a Pasteur pipette, spreading this drop and then placing the plate in an oven at 100 ° C to dry this deposit.

As can be seen in FIG. 4, which corresponds to an image taken at the SEM of the graphite plate after drying of the deposit, the film obtained is homogeneous and shows good coalescence of the PEI particles.

On the other hand, the ability of the dispersion 1 to form a film on a substrate is also tested by sizing multifilament carbon fibers (IM7 fibers with 12,000 filaments - HEXCEL) with this dispersion.

This size is produced using the device 10 which is illustrated schematically in FIG. 5 and which comprises:

a tank 11 which is filled with a sizing bath 12 (here, the dispersion 1);

a coil 13 which is situated upstream (in the direction of travel of the carbon fibers in the device 10) of the tank 11 and on which are wound the carbon fibers 14 before their introduction into the sizing bath;

an oven 15 which is situated downstream of the tank 11 and which makes it possible to dry the carbon fibers at their exit from the sizing bath;

a coil 16 which is located downstream of the oven 15 and on which are wound the carbon fibers at their outlet from this oven; and a drive system comprising in particular a set of pulleys 17 and ensuring the running of the reinforcing fiber strands from the spool 13 to the spool 16.

The temperature of the oven is set at 200 ° C so that it is lower than the glass transition temperature of the PEI.

Two speeds of travel of the carbon fibers in the device 10 are used: 10 m / min on the one hand, and 15 m / min on the other hand.

The results are illustrated in FIGS. 6A, 6B, 7A, 7B, 8A and 8B which correspond to images taken at the M EB:

filaments of carbon fiber having been sized at the running speed of 10 m / min (Figs. 6A and 6B);

filaments of a carbon fiber having been sized at the running speed of 15 m / min (FIGS. 7A and 7B); and for comparison

filaments of a carbon fiber that has not been sized (FIGS. 8A and 8B).

These images show that a size of multi-filamentary carbon fibers with the dispersion 1 leads to the formation on the filaments of these fibers of a homogeneous film, with a very good coalescence of the PEI particles present in this dispersion.

EXAMPLE II: Aqueous dispersion of particles of a polyethersulfone:

11-3- - Preparation of the dispersion:

An aqueous dispersion of particles of a polyethersulfone (PES 4100 P-SUM IMOTO Chemical), hereinafter referred to as dispersion 2, is prepared by proceeding as described in point 1.1 above, except that the PEI is replaced by PES, which forms a stable dispersion in the organic solvent. This PES has a glass transition temperature of 225 ° C. II.2 - Properties of the dispersion:

Dispersion 2 shows:

particles whose mean intensity diameter and polydispersity index, as determined by dynamic light scattering, are 158 nm and 0.210, respectively;

- a stability, as appreciated by visual observation, from 10 to

12 hours.

Furthermore, as shown in FIG. 9, which corresponds to an image taken at the SEM of a graphite plate treated with a drop of the dispersion 2 as described in point 1.2 above, this dispersion makes it possible to form a homogeneous film of PES on the surface of a substrate.

EXAMPLE III: Aqueous dispersion of particles of a polysulfone:

III.1 - Preparation of the dispersion:

An aqueous dispersion of particles of a polysulfone (PSU Ultrason ™ S 2010 Natural - BASF), hereinafter referred to as dispersion 3, is prepared by proceeding as described in point 1.1 above, except that the PEI is replaced. by the PSU. This PSU has a glass transition temperature of 187 ° C.

III.2 - Properties of the dispersion:

Dispersion 3 shows:

particles whose mean intensity diameter and polydispersity index, as determined by dynamic scattering of light, are respectively 178 nm and 0.297;

- a stability, as appreciated by visual observation, from 10 to

12 hours.

Moreover, as shown in FIG. 10, which corresponds to an image taken at the SEM of a graphite plate having been treated with a drop of the dispersion 3 as described in point 1.2 above, this dispersion also makes it possible to form a homogeneous PSU film on the surface of a substrate. REFERENCES CITED

[1] Broyles et al., Polymer 1998, 39 (15), 3417-3424

[2] FR-A-2,960,878;

[3] Giraud et al., Applied Surface Science 2013, 266, 94-99

[4] Cates et al., Journal of Physics: Condensed Matter 1990, 2, 6869-6892

[5] Hassan et al., Current Science 2001, 80 (8), 980-989

[6] Walker, Current Opinion in Colloid & Interface Science 2001, 6, 451-456

Claims

1. Use of giant micelles as rheofluidifying agent in an aqueous dispersion of particles of at least one thermoplastic polymer.

2. Aqueous dispersion of particles of at least one thermoplastic polymer, characterized in that it comprises giant micelles which are located around the particles of the thermoplastic polymer (s).

3. Use according to claim 1 or aqueous dispersion according to claim 2, characterized in that the giant micelles comprise molecules of a cationic or zwitterionic surfactant.

4. Use or aqueous dispersion according to claim 3, characterized in that the surfactant is a cationic surfactant with quaternary ammonium group, preferably an alkyltrimethylammonium salt of formula (C _n H2n + i) N ⁺ (CH3) 3, X ^", wherein n is greater than or equal to 10 and ^X" is an inorganic or organic against ion, and more preferably, a salt of hexadecyltrimethylammonium.

5. Use or aqueous dispersion according to claim 4, characterized in that the hexadecyltrimethylammonium salt is hexadecyltrimethylammonium chloride.

6. Use or aqueous dispersion according to any one of claims 3 to 5, characterized in that the giant micelles further comprise an inorganic or organic salt or an organic acid.

7. Use or aqueous dispersion according to claim 6, characterized in that the organic acid is salicylic acid.

8. Use according to any one of claims 1 to 7 or aqueous dispersion according to any one of claims 2 to 7, characterized in that the thermoplastic polymer or polymers are chosen from polyaryletherketones, polyethyleneimines, polyolefins, polyamides polyimides, thermoplastic polyurethanes, phenylene polysulfides, ethylene or butylene polyterephthalates, polysulfones, polycarbonates, polyvinyl chlorides and mixtures thereof.

9. Use or aqueous dispersion according to claim 8, characterized in that the thermoplastic polymer or polymers are chosen from polyaryletherketones, polyetherimides and polysulfones.

10. Use or aqueous dispersion according to claim 9, characterized in that the giant micelles are formed of a mixture of hexadecyltrimethylammonium chloride molecules and salicylic acid, preferably equimolar.

11. Use or aqueous dispersion according to claim 10, characterized in that the concentration of the mixture in the aqueous dispersion ranges from 5 mmol / L to 100 mmol / L and preferably from 40 mmol / L to 50 mmol / L.

12. Use according to any one of claims 1 to 11 or aqueous dispersion according to any one of claims 2 to 11, characterized in that the mass content of the aqueous dispersion of particles of the thermoplastic polymer or polymers is 0.1 from 1% to 1% and preferably from 0.4% to 0.6% relative to the total mass of the aqueous dispersion.

13. Process for the preparation of an aqueous dispersion of particles of at least one thermoplastic polymer as defined in any one of Claims 2 to 12, characterized in that it comprises: a) contacting, with stirring, an organic phase comprising the thermoplastic polymer or polymers dissolved or dispersed in an organic solvent, immiscible with water, with an aqueous phase comprising giant micelles; and

b) evaporation of the organic solvent;

whereby the transfer in the form of particles of the thermoplastic polymer (s) from the organic phase to the aqueous phase is obtained.

14. The method of claim 13, characterized in that steps a) and b) are performed simultaneously, the organic solvent is preferably a volatile solvent at room temperature.

15. Use of an aqueous dispersion of particles of at least one thermoplastic polymer as defined in any one of claims 2 to 12 for coating at least one substrate with a thermoplastic film.

16. Use according to claim 15, for the sizing of reinforcing fibers for thermoplastic matrix composite materials.

17. Use according to claim 16, characterized in that the reinforcing fibers are selected from glass fibers, carbon fibers, graphite fibers, silica fibers, metal fibers, ceramic fibers, organic fibers synthetic, natural organic fibers and mixtures thereof and, preferably, among the carbon fibers.

18. Use according to claim 16 or claim 17, characterized in that the size of the reinforcing fibers comprises immersing the reinforcing fibers in the aqueous dispersion and then drying the reinforcing fibers.